1. Technical Field
The present disclosure relates to tactile sensors for robotic applications and more particularly to manufacturing processes for and structural design of robotic tactile sensors.
2. Discussion of Related Art
As the field of robotics progresses towards autonomy, advanced tactile sensors are pivotal in enabling safe and dexterous interaction between a robot and its environment [1, 2]. Robotic tasks that generally rely on vision alone, such as grasping, are greatly enhanced with the addition of tactile sensing [3]. Shear force sensing in addition to normal force sensing is especially important in detecting slip of a grasped object [4]. Other wearable systems such as exoskeletons [5], shoes [6, 7], and gloves [8, 9] also stand to benefit from affordable, sensor rich “robot skins” that provide real-time force vectors over a large area. Over the past three decades, notable progress has been made in the field of tactile, sensing. Camera-based tactile sensors, in which a soft material is pressed and the deformation is processed visually, have been be to achieve micro-scale spatial resolution but such camera-based tactile sensors are typically limited to a small sensing area and have large, specialized hardware [10]. More compact and versatile sheets of tactile sensor arrays have also been developed [11], and leverage MEMS manufacturing to create micro-scale sensor geometries essential to multi-axis sensing. However, this method typically results in laborious and complicated multilayer assembly with sub newton force ranges [12]. MEMS manufacturing also limits the sensing area to that of a silicon wafer [13]. Other tactile sensors which have large sensing areas have been limited to normal force sensing only [14, 15], or have had limited flexibility [16], micro-fluidic eutectic indium gallium (eGaln) tactile sensors have achieved remarkable flexibility but are potentially hazardous if ruptured [17]. Therefore, there is a need for a flexible, large area tactile sensor array capable of shear force sensing in addition to normal force sensing. The transduction method also plays an important role in the design and performance of tactile sensors. Flexible tactile sensor arrays typically utilize parallel-plate style capacitors [18], or resistive serpentines or strips to detect applied loads [19]. Elastomer-based piezoresistive sensors tend to suffer from electromechanical hysteresis [20, 21] and capacitive sensors [11, 22] require significant efforts in shielding.